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What are the numbers?

Re: Acceptable Synthetic Oils?

There are probably more postings on the RF forums on this subject than any other; It's like politics or religion: everyone has an opinion. If you want some science (besides just following BMW's recommendations) you might check bobistheoilguy website, or go to the E39 RF board and look up some postings from "Craig in Canada."
E.g. Craig in Canada example on oil'03 525i Sapphire Blu/Grey, SP, Nav
'02 325it Orient Blu./Grey, SP, Nav
'98 323is Arctic Sil./Blk, SP
'95 M3 Cosmos Blk./Blk

The OP asked in his initial post if Mobil 1

was OK to use. Later in the thread he pointed out that the manual says to use 5W-30. I get from that he intends to use Mobil 1 5W-30...which is not a recommended oil. The way I read your post I thought you might be advising the OP that his "easier to find" Mobil 1 5W-30 was "fine".

Re: Acceptable Synthetic Oils?

I asked this same question in December when I purchased Mobil 1 0W-30 instead of my normal Mobil 1 0W-40. All the feedback was excellent, but the bottom line is that even though I was able to get Mobil 1 at a discount for 0W-30, I returned it to Walmart.. It is not the same specs as Mobil 1 0W-40. I concluded based on the feedback that it probably would have no effect on my engine because I change oil every 4K, but why not just get the right oil.
PS --AutoZone has a great sale NOW (as of last week) on Mobil 1 0W-40 on the 5 qt size, and you must buy a Mobil 1 oil filter. Since my store does not carry the Mobil 1 oil filter I just discarded the filter they gave me for another car, and still much cheaper with the deal. Check it out.

E46 motor oil

BMW states the oil spec for your motor is
A3B3 - which is for ALL seasons, long term(1year)and
high(12,000 mile) oil change intervals

BMW Castrol 5w/30
MOBIL 1 0W/40
meet that requirement

want a cleaner motor?, and prevent the dreaded
frozen crankcase vent system freeze-up? and
engine damage resulting from that? - then
change the oil and filter at least every 6-months,
or a max of 5,000 miles - if you plan
on keeping your car running

please expand yer question

Filter

No, the filter can not correct the use of a poor oil choice. Regardless of which filter you use, it will not change the proporties of the oil. Use the correct oil.
BUT--also use a good filter to keep the oil clean.

Let me re-phrase the question

Given use of proper oil (LL01) and a good filter (Mann/Mahle). How would more frequent filter changes help with the condensation related sludge buildup in the crank case ventilation system? I guess what I am getting at is that sludge is condensation related and not because of debris in the oil ... or is it?